Abstract

The ultimate fate of (fossil fuel) CO2 emitted to the
atmosphere is governed by a range of sedimentological and geological
processes operating on timescales of up to the ca. hundred thousand year
response of the silicate weathering feedback. However, how the various
geological CO2 sinks might saturate and feedbacks weaken in
response to increasing total emissions is poorly known. Here we explore
the relative importance and timescales of these processes using a 3-D
ocean-based Earth system model. We first generate an ensemble of 1 Myr
duration CO2 decay curves spanning cumulative emissions of up
to 20,000 Pg C. To aid characterization and understanding of the model
response to increasing emission size, we then generate an impulse
response function description for the long-term fate of CO2
in the model. In terms of the process of carbonate weathering and
burial, our analysis is consistent with a progressively increasing
fraction of total emissions that are removed from the atmosphere as
emissions increase, due to the ocean carbon sink becoming saturated,
together with a lengthening of the timescale of removal from the
atmosphere. However, we find that in our model the ultimate CO2
sink—silicate weathering feedback—is approximately invariant with
respect to cumulative emissions, both in terms of its importance (it
removes the remaining excess ~7% of total emissions from the atmosphere)
and timescale (~270 kyr). Because a simple pulse-response description
leads to initially large predictive errors for a realistic time-varying
carbon release, we also develop a convolution-based description of
atmospheric CO2 decay which can be used as a simple and efficient means of making long-term carbon cycle perturbation projections.

Research areas

Download statistics

Documents

Documents

Rights statement: This is the final published version of the article (version of record). It first appeared online via AGU at http://onlinelibrary.wiley.com/doi/10.1002/2014GB005074/abstract. Please refer to any applicable terms of use of the publisher.